The present invention relates generally to power source filters, and more particularly to filters for suppressing noise from ac power sources used to energize audio video electrical equipment.
Audio and video electrical equipment such as audio amplifiers, video camera recorders, televisions, and the like (collectively referred to herein as xe2x80x9caudio videoxe2x80x9d equipment, whether solely audio, solely video, or a combination thereof) typically are energized with standard alternating current (ac) power operating at 120 volts and a frequency of 60 Hertz. It happens that electrical noise is often present in the power that is supplied to audio video equipment, and this electrical noise can degrade the performance of the equipment that it energizes.
Accordingly, noise filters have been provided to suppress noise in ac power lines. As recognized by the present invention, electrical noise from an ac power source can include spurious power surges and frequency-based noise. To suppress power surges in power lines before the power surges reach the load, a filter can be provided, with the filter including a capacitor that is coupled across the power lines, in parallel with the load, at the input of the load. As understood by the present invention, however, particularly large power surges can cause the capacitor to fail, thereby rendering the filter that incorporates the capacitor inadequate for suppressing subsequent power surges. Accordingly, the present invention recognizes the desirability of providing a power line input capacitor to suppress power surges to audio video equipment, while prolonging the useful life of the input capacitor.
The present invention, in considering frequency-based noise, recognizes that noise at a particular frequency can be removed from an ac power line by providing a filter having an inductor and a capacitor arranged and tuned for suppressing signals having the frequency of the noise sought to be removed. As further recognized herein, in conventional filters a separate inductor-capacitor pair is provided for each frequency sought to be removed. In other words, to remove two frequencies, two inductor-capacitor pairs are typically provided, three pairs to remove three frequencies, and so on. The present invention understands, however, that it would be cost-effective to provide a power line filter for audio video equipment wherein a single capacitor can be used to suppress more than one noise frequency.
Accordingly, it is an object of the present invention to provide a noise filter for an ac power line to audio video equipment that suppresses noise surges. Another object of the present invention is to provide a noise filter for an ac power line to audio video equipment that prolongs the life of an input capacitor for suppressing noise surges. Still another object of the present invention is to provide a noise filter for an ac power line to audio video equipment that suppresses more than one noise frequency while minimizing the number of electrical components in the filter. Yet another object of the present invention is to provide a noise filter for an ac power line to audio video equipment that is easy to use and cost-effective to manufacture.
Other features of the present invention are disclosed or apparent in the section entitled: xe2x80x9cBEST MODE FOR CARRYING OUT THE INVENTION.xe2x80x9d
A filter is disclosed for suppressing noise in at least first and second power lines used for electrically connecting an ac power source to an audio video load, i.e., a load that produces either audio, or video, or both. The filter includes a first inductor that is coupled to the first power line in series between the power source and the load. Also, the filter includes a second inductor that is coupled to the second power line in series between the power source and the load.
In accordance with the present invention, a capacitor is coupled between an input side of the first inductor and an output side of the second inductor. With this combination, the capacitor can absorb noise surges while being somewhat protected from damage by the second inductor. Furthermore, the inductances of the inductors and the capacitance of the capacitor are established for suppressing at least two predetermined frequencies in the power lines, using only a single capacitor.
Additionally, multiple capacitor/inductor combinations can be provided for suppressing noise at additional frequencies. More specifically, a first capacitor with first and second inductors can be provided as described above, and a third inductor can be provided in series with the first inductor. Also, a fourth inductor can be provided in series with the second inductor, with a second capacitor being coupled between an input side of the third inductor and an output side of the fourth inductor. Consequently, the filter suppresses four predetermined frequencies with only two capacitors.
In another aspect, a device is disclosed for suppressing ac power line noise to an audio video load. The device includes first and second power lines configured for electrically connecting an ac power source to the audio video load. Additionally, first and second inductors are respectively coupled to the first and second power lines, and each inductor defines a respective input side and a respective output side. At least one capacitor is coupled to a capacitor line. As intended by the present invention, the capacitor line is attached to the input side of the first inductor and to the output side of the second inductor.
In still another aspect, a method for suppressing noise at the power supply input of audio video equipment that is coupled to a source of 60 Hz ac power having a first power line and a second power line includes coupling a filter to the power lines. The filter has at least one circuit which includes at least a first inductor coupled to the first power line in series between the power source and the load, and at least a second inductor coupled to the second power line in series between the power source and the load. At least a first capacitor is coupled to the first power line upstream of the first inductor and to the second power line downstream of the second inductor. With this filter, noise surges and at least two noise frequencies in one or more of the power lines are suppressed by the filter.
The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts.